The chilling power of sunlight

At this winery, the solar collector at the front drives the absorption refrigeration machine. The wine in the fermentation tanks (in the background) is cooled by a cold accumulator (Photo: Fraunhofer ISE)

The sun is already being used to power air-conditioning systems so it seems a natural progression to apply it to refrigerate perishable foodstuffs - a huge consumer of fossil fuel-based energy. Scientists from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany, are taking this task to heart with two solar refrigeration trials in the Mediterranean region – one at a Tunisian winery and the other at a dairy in Morocco.

“Our method is ideal for countries which have many days of sunshine and in remote areas where there are no conventional means of refrigeration owing to a lack of water and non-existent or unreliable energy sources. It is environmentally-friendly and reduces the use of expensive electricity for conventional refrigerators to a minimum,” says Dr Tomas Núñez, scientist at the ISE.

Solar-powered refrigeration has two-fold benefits because the refrigeration is always available when the sun shines, which also equates to when refrigeration is needed most, says Dr Núñez.

The scientists have installed concentrating collectors which direct the sunlight onto an absorber via a reflector, making it possible to convert the solar radiation into hot water with a temperature of 200°C.

“This extreme water temperature is necessary in order to drive the absorption refrigeration machine for the high external temperatures that prevail there. We do not use electricity to provide the refrigeration, we use heat. The result is the same in both cases: refrigeration in the form of cold water or – in our case – a water-glycol mixture,” he says.

As the absorption refrigeration machine produces temperatures of 0°C, so the experts use the mixture to prevent the water from freezing (the same principle as in car radiators). The water-glycol solution is collected in cold accumulators and then pumped through a heat exchanger, which cools the milk.

“We use a slightly different system for wine, with the refrigerant flowing through coiled pipes in the wine tanks,” says Dr Núñez.

“MEDISCO is a demonstration project. The system is not yet ready for the market, but I am certain it will be possible in future to use solar refrigeration on farms and in the chemical and cosmetics industries,” he says.

The project funded by the European Commission is run by the Polytechnic University of Milan.

Solar Refrigeration is very useful in Hot belt especially in Gulf, Africa, Asia and Latin America. West spends more energy on heating while east spends more energy in cooling. If a cost effective solar air conditioner can be designed that will sell like hot cake in Developing countries especially in India. Of course some Solar Airconditioning systems from China are available but they are expensive and less efficient. A world renowned Solar Energy Research Institute like Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany, can come out an efficient solar airconditioner.

Dr.A.Jagadeesh Nellore (AP), India

Dr.A.Jagadeesh

I have just wondered if wine and milk are stored in insulated tanks. They usually appear to be stainless steel towers. To help insulation, they could be buried in the ground

windykites1

Yes, thos tanks are insulated. They're doubleskinned tanks usually filled with cork, fibreglass batting or a mixture (you can't pump the gap down to a partial vacuum as air pressure would crush it.)